Drawing tube



. y 1940- E. DVORAK 2,207,245

DRAWING TUBE Filed Nov. 28 1938 2 Sheets-Sheet l Juiy 9,1940. E, DVORAK 2,207,245

- DRAWING TUBE Filed NOV. 28, 1938 2 Sheets-Sheet 2 IN Vsnroa: BMILIODWoM .7 M ATTORNEY Patented July 9,

zeomis PATENT OFFICE naawme TUBE ammo Dvorak, Turin, Italy.

Application November 2:, 1m. Scrlal No. 242,132 In Italy December 2, 1931 obtained by pull or push on a member acting on the bottom of the ingot or blank, 'which in the case of push may be the mandrel itself.

Drawing processes of this type which sharply l6 distinguish over rolling processes with driven stretching rollers have already -been proposed'for stretching tubes between loose rollers. As the publications on the subject show; these processes are based on the following premises; it is not posm sible to obtain in' each caliber formed by loose drawing rollers a reduction greater than '20 to consequently the number-of the calibers should be relatively large, that is at least equal to the elongation factor. In view of the high :5 number of calibers, the work must be treated simultaneously in a plurality of calibers because, in consideration of the. number of calibers, successive treatments would enlarge the machine beyond an admissible limit. Besides, in the case of hot drawing, one heat would no longer be sumcient. It was therefore thought necessary to prevent the tensile stresses in the zone of the wall adjacent to the bottom of the work from exceeding the breaking load, notwithstanding the simultaneous action of a large number of calibers by radual variations in the diameters of the drawing rollers.

It has now been found, as a basis of this invention, that the said premises are not correct,

it is possible, contrarily to what is said above,

to obtain in calibers formed by loose drawing rollers individual reductions of and more,

so that the number of calibers may be much smallerthan the elongation factor, with the fur- 5 ther result that on a machine of a fully admissible length and, in the case of hot drawing, with one heat the work may be successively drawn in the,various calibers formed; by the loose rollers,

so that it is no longer necessary to follow strict 5 rules with regard to the diameter of the rollers and their ratio to the diameters of the calibers.

By successive" treatments I mean the method in which the work is introduced into a succeeding caliber only after it has fully or almost fully left I the preceding caliber.

ing rollers being arranged in such manner that the edges of their operating surfaces engage the zones of reduced thickness. As a result, not even 10 reductions of 40% and more will produce at the edges of the drawing rollers longitudinal ribs or protrusions to avoid which it was heretofore thought impossible to obtain by means even of closed calibers formed by loose drawing rollers '16 a reduction exceeding 25%. According to this invention, theloose drawing rollers of each caliber are followed in a manner known per se by pressure rollers angularly displaced with respect to those producing-in a manner known per se a lo slight removal ofthe inner wall of the tube from the mandrel. This contributes in increasing the elongation obtainable because in the next caliber, the frictionbetween the inside wall of the tube and the mandrel is reduced to a practically negis ligible value, so that nearly all the power absorbed is transformed into drawing work.

Even under this aspect the process according to this invention distinguishes from previous drawing processes in which, in order to eliminate the danger of breakage above the bottom, it was thought necessary, for the work to adhere uninterruptedly to the mandrel, with the deleterious consequence that during drawing strong resistances in friction between work and mandrel had to be overcome.

As stated above, according to this invention, the work enters a caliber after it has fully or almost fully left the preceding caliber.

The invention will be explained hereinafter by 40 way of example in a more detailed manner with reference to the accompanying drawings.

Figure 1 is a longitudinal section of a unit comprising sets of rollers and of the work about to enter therebetween.

Figures 2, 3 and 4 are sections on lines 2-J2, 3-3, 4-4 of Figure 1, respectively. Q

- Figure -5 is'a section on an enlargedscale of the work and mandrel, showing the preliminary formation of the zones of reduced thickness. 50

Figure 6 is a section similar'toFlgure 5 illustrating the action of the loose drawing rollers.

Figure 7 shows by a similar sectional view the action of the pressure rollers. t,

Figure all-81) shows diagrammatically; the If manufacture of a tube in four successive calibers.

Figure 9 shows, by way of example, a section through the axes of the drawing rollers of a caliber for cold drawing.

As shown by Figures 1 and 8 manufacture of a thin-walled tube is started from a hollow thickwalled billet of which the bottom 2a is closed in the example shown.- The billet is fitted on the mandrel l and by pushing the latter is passed between the calibers. It would also be possible to provide a bottom'with a central opening and act on its inside surface by a tie-rod, by means of which the billet and later the tube is drawn through all the calibers.

A cage 6 is provided for each caliber and has on the side from which the work arrives, pairs of flanges 6a which are in the number of four in the example shown. A loose roller 3, called grooving roller because it is provided with a circular rib 3a situated exactly or approximately in the middle longitudinal plane of the caliber, is mounted in each pair of flanges 6a. Preferably, and as shown, the rib is of triangular section with rounded apex, of which the angle of aperture is variable between 5 and 180.

In the central portion of the cage 6 there are mounted by means of strong pins 4a as many loose drawing rollers 4 as there are grooving rollers 4, that is four in the example shown. The drawing rollers 4 form a closed caliber and are displaced about the axis of the caliber and with respect to the grooving rollers 3' through an angle of 360 in which n is the number of the drawing rollers. With four drawing rollers as in the example shown, the angular displacement is of 45. The operative surface of the drawing rollers 4 is exactly or approximately generated by a circular arc and merges laterally into the circular edges ib.

The cage 6 is provided at the back with further flanges 6b between which there are mounted loose pressure rollers 5 displaced through with respect to the drawing rollers 4, and each provided with a cylindrical rib 5a.

By bringing the work 2 on the mandrel through the rollers 3, the ribs- 3a produce on the outer surface of the tube in formation four longitudinal grooves (Figure 5) uniformly arranged at the periphery, reducing by sections the wall approximately to the thickness that it is desired to obtain in the respective caliber. The grooved work comes then under the loose drawing rollers 4. On account of the angular displacement through the edges to of the operative surfaces of the drawing rollers 4 meet over the longitudinal grooves I, as will be seen from Figure 6. This prevents the formation of fins and protrusions that might be cessive grooves 1 which, as said above, makes a very strong reduction possible.

The work is then submitted to the action of the ribs 5a of the pressure rollers 5 (Fig. 7). By effect of the angular displacement through these rollers act on the work in the direction of the bisectrices between the longitudinal middle lines of the drawing rollers 4. This produces in a manner known per se a removal of the inside surface of the work 2 from the mandrel I, so that the work may be freely displaced on the mandrel when it is subjected to the next drawing stage.

As shown in Figures 8a and 8b, the work comes into a caliber only after its rear end has left the preceding caliber. By calling L the length of the billet and assuming a 50% drawing in each caliber, the distance between the calibers I and II is 2L, the distance between the calibers II and III is 4L, the distance between the calibers III and IV is 8L, while the length of the tube obtained in the fourth caliber is 16L. In most practical cases, in which soft steel tubes are manufactured, it will be possible to obtain with the process according to this invention an elongation 16:1 in four calibers.

The method according to this invention is carried out preferably in the hot and, in consideration of the limited number of calibers required, with one heat only, although operation in the different calibers may be carried out successively and not simultaneously.

In certain cases the process may be carried out in the cold. As this requires very smalldrawing rollers, while the pressures occurring are very high, according to Figure 9 the small drawing rollers 4' are provided with thin pivots 4a. only for maintaining them in position, while the pressures are absorbed by rollers 9 backing the drawing rollers 4'. The rollers 9 are mounted by means of strong pivots 9a. and rolling bearings in separate members l0 fitted by the rollers 9 in radial slots in the strong body portion 8 and fixed to the latter by means of screw-threaded bolts or the like. I

What I claim is:

1. The method of drawing tubes from hollow blanks fitted on a mandrel comprising drawing longitudinal grooves in sections distributed on the outside of the work, drawing the work through a caliber formed by freely rotatable drawing rollers arranged in such manner that the edges of their operative surfaces meet over the longitudinal grooves previously formed in the work, drawing the work through freely rotatable pressure rollers arranged around the work in angular displacement with reference to the said drawing rollers in order to slightly enlarge the diameter of the work and to thus separate the inside wall of the work from the mandrel, the foregoing operations being performed at the first work station, and repeating said. operations at successive work stations spaced apart a distance at least greater than the length of the work on the mandrel after having passedthrough the preceding work station.

2. The method of drawing tubes from hollow blanks fitted on a mandrel comprising drawing longitudinal grooves in sections distributed on the outside of the work by drawing the work through freely rotatable grooving rollers, drawing vthe work through a caliber formed by freely rotatable drawing rollers having concave work faces arranged in such manner that the edges of their respective work surfaces meet over the longitudinal grooves previously formed in the work, drawing the work through freely rotatable cylindrical pressure rollers aranged around the work in angular displacement with reference to the said drawing rollers in order to slightly enlarge the diameter of the work and to thus separate the inside wall of the work from the mandrel.

3. A machine for drawing tubes from hollow blanks fitted on a mandrel, comprising a set of freely rotatable grooving rollers adapted to groove the work longitudinally, a second set of rollers having concave work faces and comprising a plurality of freely rotatabledrawing rollers displaced in a peripheral direction around the work in such manner that the edges of the drawing rollers meet over the grooves in the work produced by the grooving rollers, and a third set of freely rotatable substantially cylindrical pressure rollers adapted to slightly enlarge the diameter of the work and thereby free the inner inside wall of the'work from the mandrel, said set of pressure rollers being displaced in a pressure rollersare effective over the area of the work which has passecbbeneath the edges of the.

drawing rollers; the foregoing .three sets of rollers comprising a drawing unit, a plurality of said units, the distances between the units being 7 such that the work enters a succeeding unit after having passed entirely through a preceding unit.

4. A machine for drawing'tubes from hollow blanks comprising ,a" substantially .cylirfdrical mandrel, a set of freely rotatable grooving rollers adapted to groove the work longitudinally, a second set of rollers having concave work faces and comprising a plurality of freely rotatable drawing rollers displaced in a peripheral direction around the work in such manner that the edges of the drawing rollers meet over thegrooves in the work produced by the grooving rollers, and a third set of freely rotatable substantially cylindrical pressure rollers adapted to slightly enlarge the diameter of the work and thereby free the inner inside wall of the work from the mandrel, said set of pressure rollers'being displaced in a peripheral direction around the work relative to the drawing rollers in such manner that the pressure rollers are eif'ective over'the area of the work which has passed beneath the edges of the drawing rollers to slightly enlarge the diameter of the work and free the same from the mandrel.

' EMILIO DVORAK. 

